EKG Interpretation

Objectives Review approach for reading EKGs Keep it simple Impress preceptors on rounds

Resources

Interpretation Rate Rhythm Axis Hypertrophy Ischemia, Injury, Infarction

Rate Count # of large boxes between 2 successive R-waves: 1 box = 300 bpm 2 boxes = 150 bpm 3 boxes = 100 bpm 4 boxes = 75 bpm 5 boxes = 60 bpm 6 boxes = 50 bpm 7 boxes = 43 bpm 8 boxes = 37 bpm

Irregular rhythms If the R-R Interval is irregular: Count the number of QRS complexes in a 10 sec span (that is on the entire EKG) and multiply it by 6! {or no. of QRS complexes in a 6 sec span multiplied by 10}

Rhythm Determine whether sinus or non-sinus

Sinus Rhythm Every QRS preceded by P-wave P-wave has normal morphology Duration <0.12 sec (<3 boxes) Height <2.5 mm P-wave has normal axis Upright in lead II Sinus “arrhythmia” Rate varies with respiration

Arrhythmias Irregular rhythms Escape rhythms Premature beats Tachy-arrhythmias Heart blocks

Irregular rhythms Wandering atrial pacemaker P wave shape varies Atrial rate <100 Irregular ventricular rhythm Multifocal atrial tachycardia Same as above, but rate>100 Atrial fibrillation / flutter

Escape rhythm Junctional escape Ventricular escape Originates in AV junction Narrow QRS (<0.10ms) Rate 40-60 Ventricular escape Originates in ventricles Wide QRS (not normal depolarization) Rate 20-40

Junctional escape

Premature beats Irritable focus spontaneously fires a single stimulus Atrial (PAC) Ventricular (PVC)

Paroxysmal tachycardia A very irritable focus suddenly paces rapidly Paroxysmal atrial tachycardia Paroxysmal junctional tachycardia Paroxysmal ventricular tachycardia Look for presence/absence of P waves and ventricular appearance to determine type

Supraventricular tachycardia Often can’t tell between PAT and PJT (both originate above ventricles & produce narrow QRS) Rapid PAT can be so rapid that P waves not visible Supraventricular tachycardia (SVT) is umbrella term for both

Flutter vs fibrillation Flutter caused by single ventricular focus firing rapidly (250-350x/min) Fibrillation caused by multiple foci firing rapidly (350-450x/min)

Atrial flutter & fibrillation Atrial fire so rapidly not every impuse triggers ventricular contraction 2:1, 3:1, 4:1 block, etc Atrial fibrillation Irregularly irregular

Ventricular flutter & fibrillation Ventricular flutter has smooth sine-wave appearance with no jagged waves Often degenerates into ventricular fibrillation

Heart blocks AV block Bundle branch block

AV block 1st degree: delay in normal AV conduction PR >0.20 sec 2nd degree: interruption in normal AV condution 3rd degree: complete dissocation in AV conduction

1st degree AV block PR >0.20 sec

2nd degree AV block Type I (Mobitz I) aka Wenckebach PR progressively gets longer with each beat QRS complex is dropped Cycle repeats Type II (Mobitz II) PR stays constant, then one beat isn’t conducted

2:1 AV block Sometimes hard to tell Wenckebach vs Mobitz II apart if both have 2:1 conduction (2 P waves then QRS) Wenckebach Likely if PR interval lengthened and QRS normal Mobitz II Likely if PR interval normal and QRS widened

3rd degree AV block Complete dissocation between atria & ventricles Atria fire regularly Ventricles contract independently at either junctional escape (40-60) or ventricular escape (20-40) If above AV nodal junction, then junctional escape rhythm occurs

Bundle branch block Wide QRS (<0.12 sec) Left Right Incomplete RR’ in V5 & V6 Right RR’ in V1 & V2 Incomplete QRS 0.10-0.12 sec

Left bundle branch block

Right bundle branch block

Axis Measures overall electrical activity of heart Limb leads (I, aVF) used to quickly determine axis Lead I: 0 degrees aVF: +90 degrees

Axis

If lead I is positive, the green zone reveals the area of electrical activity Lead I -90 _ + I aVF

red zone reveals the area of electrical activity aVF If aVF is positive, the red zone reveals the area of electrical activity – -90 + I aVF

If we superimpose these onto one another we find the axis to be -90 I If we superimpose these onto one another we find the axis to be between 0° & +90° aVF +90

Left axis deviation Usually caused by HTN, aortic valvular disease & cardiomyopathies aVF: negative Lead I: positive

If lead I is positive then the blue zone is the area of electrical activity Lead I _ -90 + I aVF +90

If aVF is negative, the green zone is the area of electrical activity _ aVF If aVF is negative, the green zone is the area of electrical activity -90 + I aVF +90

If we superimpose these onto one another we find the axis to be between 0° & –90° -90 I aVF +90

Right axis deviation Usually secondary to enlarged right ventricle or pulmonary disease Pulmonary HTN COPD Acute pulmonary embolism

If lead I is negative the green zone encompasses the area of electrical activity Lead I _ -90 + I 180 aVF +90

red zone reveals the area of electrical activity aVF _ If aVF is positive, the red zone reveals the area of electrical activity aVF -90 + I 180 aVF +90

If we superimpose these onto one another, we find the axis to be -90 I 180 If we superimpose these onto one another, we find the axis to be between 90° & 180° aVF +90

Right atrial enlargement

Left atrial enlargement

Left ventricular hypertrophy Large S in V1 Large R in V5 S in V1 + R in V5 >35mm = LVH aVL > 11-13mm = LVH

Right ventricular hypertrophy Normally S > R in V1 Large R in V1 = RVH Large R in V1 will get smaller V2V4

Ischemia, Injury, Infarction T wave inversions or ST depression Injury ST segment elevation >1mm in 2 or more contiguous leads Infarction Q waves 1mm wide or 1/3 height of QRS

Ischemia

Injury

Infarction

Location Anterior = V1-V4 Inferior = II, III, aVF Lateral = I, aVL Posterior = Large R wave, ST depression in V1 or V2

Anterior MI

Inferior MI

Anterolateral

Posterior MI

Tips for rounds Review EKG silently (don’t talk though method unless asked to) Ignore interpretation at top of 12-lead Intervals usually ok Summarize findings Rate Rhythm Axis Hypertrophy Ischemia, infarction

Example This is a normal sinus rhythm, rate 60, normal intervals, no hypertrophy, no ischemic or infarctive changes This is normal sinus rhythm, rate 75, 1st degree AV block, left ventricular hypertrophy, possible old inferior MI This is atrial fibrillation with a rapid ventricular response

NSR Rate 80 Normal axis Normal intervals, no block No hypertrophy No ischemic or infarctive changes

NSR (sinus tachycardia) Rate 111 Normal axis Normal intervals One premature ventricular contraction No hypertrophy No ischemic or infarctive changes

NSR, rate 100 1st degree AV block Normal axis Borderline LVH by voltage No ischemic or infarctive changes

NSR, rate 100 LAD Normal intervals No hypertrophy Acute anterior wall MI with reciprocal ST depression inferiorly

NSR, rate ~60 Normal axis Right bundle branch block No hypertrophy No ischemic or infarctive changes

NSR, rate ~90 Normal axis Normal intervals No hypertrophy Old inferior wall MI with ?inferior ischemia

Atrial flutter with variable block Normal QRS (no BBB) No hypertrophy No ischemic or infarctive changes

NSR, rate 75 Left axis deviation Left bundle branch block Left ventricular hypertrophy Can’t tell infarction because of LBBB repolarization changes

Ventricular tachcardia Rate ~170 Don’t really care about anything else

Accelerated junctional Normal axis LVH by voltage No ischemic or infarctive changes

Interpretation Rate Rhythm Axis Hypertrophy Ischemia, Injury, Infarction